Below is the circuit diagram of a microphone audio amplifier using LM386 ic.
This circuit amplify weak audio signal from an electret microphone and drive a small 4/8 ohm speaker or can be used as a pre-amplifier stage of an audio amplifier.
Working
- Electret Microphone convert sound to weak analog electrical signal.
- R1(10K) provides bias voltage to power internal FET amplifier inside the Electret mic.
- C1(10uF) block the DC voltage and allow only AC audio signal to reach the amplifier.
- C3(10uF) between pin 1 and pin 8 set the gain of this amplifier to 200 without this capacitor gain will be 20. By adding a POT in series with this capacitor , you can make gain adjustable from the 20 to 200.
- POT(100k) adjust the volume.
- C4(220uF) block DC voltage reaching the speaker (typically 1/2 of power supply voltage will be available at Vout pin. In this case of 9V it’ll be 4.5V at pin 5(Vout) ). This capacitor form a high pass filter with speaker and only allow frequency above 90hz to pass though it.
- Speaker – 4 or 8 ohm speaker can be used.
You can also use this circuit as a microphone preamplifier by removing the speaker and connecting the negative side of C4 capacitor to the input of your main power amplifier (like a TDA2030, TDA7297, or any audio amp).